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Acta Univ. Palacki. Olomuc., Gymn. 2010, vol. 40, no. 2
SPECTRAL ANALYSIS OF HEART RATE VARIABILITY IN PATIENTS
WITH SPINAL CORD INJURY
Petr Uhlíř, Jaroslav Opavský, Amr Zaatar, Milada Betlachová
Faculty of Physical Culture, Palacký University, Olomouc, Czech Republic
Submitted in February, 2010
BACKGROUND: Yearly, 200–300 new spinal cord injuries (SCI) happen in the Czech Republic. Some of these
patients suffer from autonomic disturbances, especially concerning their cardiovascular and genito-urinary systems.
Autonomic disturbances markedly decrease quality of life in patients with SCI. It is important to assess the severity
of the autonomic nervous system (ANS) involvement in these subjects.
OBJECTIVE: The main aim of this study was to assess the spectral analysis of heart rate variability as a marker
of cardiovascular autonomic regulation in patients with spinal cord injury and to compare it with findings in healthy
controls.
METHODS: Ten paraplegics (with a mean age of 53.1 ± 15.8 years, seven males and three females) participated
in this study. There were five patients with incomplete and five patients with complete spinal cord injury. The ASIA –
American Spinal Injury Association, the modified Ashworth scale and the Questionnaire on Autonomic Functions
were used. Autonomic reactivity was evaluated by means of the spectral analysis of heart rate variability (SAHRV)
method (short-term registration) using the supine-sitting-supine test. Diagnostic system VarCor PF7, which is an innovation of the VarCor PF6 system, was used. Twenty four healthy subjects (with a mean age of 51.9 ± 9.4 years) were
enrolled as a control group.
RESULTS: A marked decrease of the reactivity of the autonomic nervous system as a response to orthostatic
changes was found in patients after SCI (paraplegics). In particular, characteristic responses of low frequency (LF)
and high frequency (HF) spectral components during the body position changes were suppressed in these patients in
comparison with healthy controls. Furthermore, a significant decrease in the spectral power of the LF and HF components was found in patients after SCI. The value of the spectrum’s total power (TP) was significantly lower in the
group of paraplegics in comparison with healthy volunteers, both in the first and in the repeated supine positions. A significant degree of orthostatic hypotension was registered only in two paraplegics in a sitting position. A lower increase
in the LF/HF ratio was registered in a sitting position in a group of paraplegics in comparison with healthy subjects.
CONCLUSIONS: A decrease in the reactivity of the autonomic nervous system to orthostatic changes, which
evidences disturbances of cardiovascular regulation, was found in patients after spinal cord injury (paraplegics). The
reduction of the low-frequency component (LF) of the spectral analysis of heart rate variability reflects a lowered
sympathetic activity in these patients in a sitting position. It reflects ortostatic disturbances in situations with body
position changes associated with a modified orthostatic load. Blood pressure measurement and SAHRV contribute
to a more precise assessment of the autonomic dysfunction in patients after SCI.
Keywords: Spinal cord injury, spectral analysis, heart rate variability, autonomic nervous system.
INTRODUCTION
Yearly, 200–300 new spinal cord injuries (SCI) happen in the Czech Republic. Some of these patients suffer from autonomic disturbances, especially concerning
their cardiovascular and genito-urinary systems. Autonomic disturbances markedly decrease quality of life in
patients with SCI. It is important to assess the severity
of the autonomic nervous system (ANS) involvement in
these subjects. The assessment of heart rate variability
(HRV) with the use of the spectral analysis of heart
rate variability (SAHRV) represents a method available
in clinical practice. Using computer based programs,
specific frequency bands and their oscillations can be
quantified to estimate vagal and sympathetic activity
contributions to heart rate.
A relatively low number of studies concerning autonomic nervous system function in subjects with spinal
cord injury focused on this topic can be found in the
literature (Bunten et al., 1998; Claydon et al., 2008;
Chen et al., 2006; Wecht et al., 2003). The main aim of
this study was to assess heart rate variability as a marker
of cardiovascular autonomic regulation in patients with
spinal cord injury and to compare it with findings in
healthy controls.
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Acta Univ. Palacki. Olomuc., Gymn. 2010, vol. 40, no. 2
MATERIAL AND METHODS
al., 2005). The ECG signal was processed in PC with
the use of special software for this diagnostic system
(Salinger et al., 2005).
Twenty four healthy subjects (with a mean age of
51.9 ±9.4 years) were enrolled as a control group. Blood
pressure values in the first supine position and at the
end of their stay in the sitting position were measured.
Ten paraplegics (with a mean age of 53.1 ±15.8 years,
seven males and three females), participated in this study.
There were five patients with incomplete and five patients
with complete spinal cord injury. The ASIA – American
Spinal Injury Association (Wise, 2009), modified Ashworth scale (Bohannon & Smith, 1987), and the Questionnaire on autonomic functions (Opavský, 2002) were
used. Autonomic reactivity was evaluated by means of
the SAHRV method in the supine-sitting-supine test (SSS
test), which is a modification of the supine-standing-supine
test (Opavský, 2002; Salinger, 1999). SAHRV was used as
a sensitive, non invasive method for the evaluation of autonomic nervous system activity. The areas of the frequency
spectrum are divided into three major components:
1. VLF (very low frequency, from 20 to 50 MHz) component, its origin hasn’t been fully explained, yet.
2. The LF (low frequency, from 50 to 150 MHz, mainly
about 100 mHz) component is explained mostly as
a reflection of arterial baroreceptor sympathetic activity (Pagani et al., 1992).
3. HF (high frequency from 150 to 400 MHz) component represents a vagal activity associated with breathing (Malik & Camm, 1990).
RESULTS
A marked decrease in the reactivity of the autonomic
nervous system to orthostatic changes was found in patients after SCI (paraplegics). In particular, characteristic responses of low frequency (LF) and high frequency
(HF) spectral components during changes of body positions were suppressed in comparison with healthy controls (Fig. 1 and Fig. 2).
Furthermore a significant decrease in spectral power
of the LF and HF components was found in these patients (TABLE 1 and TABLE 2). The value of the total
power (TP) was significantly lower in the group of paraplegics in comparison with healthy volunteers, both in
the first and in the repeated supine positions (TABLE 3
and Fig. 3). A significant orthostatic hypotension was
registered only in two paraplegics when in a sitting position. A lower increase in LF/HF ratio was registered in
a sitting position in a group of paraplegics in comparison with healthy subjects (TABLE 4 and Fig. 4).
Diagnostic system VarCor PF7, which is innovation
of the system of VarCor PF6, was used. The ECG signal
is obtained with the help of an electrode belt POLAR
or electrodes placed on the thorax. A transmitter of this
system works at a frequency of 433 MHz. (Štěpaník et
Fig. 1
Spectral power of the LF component in a group of paraplegics and age-matched healthy controls in the supine-sittingsupine test
Power LF-paraplegics
Power LF-control group
350
Power LF [ms 2]
300
250
200
150
100
50
0
1
2
3
Positions of the body in the supine(1)-sitting(2)-supine(3) test
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Acta Univ. Palacki. Olomuc., Gymn. 2010, vol. 40, no. 2
Fig. 2
Spectral power of the HF component in a group of paraplegics and age matched healthy controls in the supine-sittingsupine test
Power HF-paraplegics
Power HF-control group
Power HF [ms2]
600
500
400
300
200
100
0
1
2
3
Positions of the body in the supine(1)-sitting(2)-supine(3) test
TABLE 1
Spectral power of the LF component in a group of paraplegics and age-matched healthy controls in the supinesitting-supine test
LF [ms2]
1
2
3
mean
SD
mean
SD
mean
SD
PARA
53.8
30.3
51.5
42.8
61.8
40.4
CONTR
293.1
378.6
328.1
350.7
283.2
398.5
TABLE 2
Spectral power of the HF component in a group of paraplegics and age matched healthy controls in the supinesitting-supine test
p
0.001
HF [ms2]
1
0.0013
2
0.003
3
mean
SD
mean
SD
mean
SD
Legend:
body positions in the supine-sitting-supine test: 1 – supine, 2 – sitting, 3 – repeated supine
PARA = paraplegics
CONTR = control group
LF = low frequency component of the spectral analysis of a heart rate variability (0.05–0.15 Hz)
Power LF [ms2] = spectral power of the LF component of the SAHRV
HF = high frequency component of the spectral analysis of a heart rate variability (0.15–0.4 Hz)
Power HF [ms2] = spectral power of the HF component of the SAHRV
p = level of significance
PARA
38.0
27.5
34.0
43.7
56.4
50.3
CONTR
387.9
639.6
169.8
333.2
539.3
830.9
p
0.0004
0.03
0.001
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Acta Univ. Palacki. Olomuc., Gymn. 2010, vol. 40, no. 2
TABLE 3
Total spectral power (TP) in a group of paraplegics and age-matched healthy controls in the supine-sitting-supine test
TP [ms2]
1
2
3
mean
SD
mean
SD
mean
SD
PARA
91.8
53.3
85.5
67.0
115.6
80.8
CONTR
705.8
949.4
524.9
717.9
840.3
1218.6
p
0.008
0.007
Fig. 3
Total spectral power (TP) in a group of paraplegics and age-matched healthy controls in the supine-sitting-supine test
Total Power [ms 2]
Total Power-paraplegics
Total Power-control group
900
800
700
600
500
400
300
200
100
0
1
2
3
Position of the body in the supine(1)-sitting(2)-supine(3) test
Legend:
body positions in the supine-sitting-supine test: 1 – supine, 2 – sitting, 3 – repeated supine
PARA = paraplegics
CONTR = control group
Total power [ms2] = sum of the spectral power of the low frequency (LF) + high frequency (HF) components
p = level of significance
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Acta Univ. Palacki. Olomuc., Gymn. 2010, vol. 40, no. 2
TABLE 4
Ratio LF/HF in a group of paraplegics and age-matched healthy controls in the supine-sitting-supine test
LF/HF
1
2
3
mean
SD
mean
SD
mean
SD
PARA
1.9
1.0
2.6
2.2
1.8
1.4
CONTR
1.6
1.4
4.8
5.1
1.4
1.6
p
N.S.
N.S.
N.S.
Fig. 4
Ratio LF/HF in a group of paraplegics and age-matched healthy controls in the supine-sitting-supine test
LF/HF-paraplegics
LF/HF-control group
6
LF/HF
5
4
3
2
1
0
1
2
3
Positions of the body in the supine(1)-sitting(2)-supine(3) test
Legend:
body positions in the supine-sitting-supine test: 1 – supine, 2 – sitting, 3 – repeated supine
PARA = paraplegics
CONTR = control group
LF/HF = ratio of the low frequency (LF) and high frequency (HF) spectral power
p = level of significance
N.S.= non significant
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Acta Univ. Palacki. Olomuc., Gymn. 2010, vol. 40, no. 2
TABLE 5
Questionnaire on autonomic functions in paraplegics
A ratio A/B (7.6:6.9) in paraplegics demonstrates
a minimal (non significant) prevalence of responses for
sympathetic function.
Decreased autonomic reactivity in patients after SCI
shows a markedly decreased adaptation to orthostatic
load. SCI patients are known to suffer from autonomic
failure as a result of their injury (Bunten et al., 1998).
We have described disturbed cardiovascular control in
subjects after SCI, both in a supine position and during
a situation with orthostatic load (sitting position).
A significant decrease in the power of LF and HF
spectral components (in frequency domain) in patients
after SCI (paraplegics) was found in our study. It corresponds to the results published by Ditor et al. (2005).
Furthemore, a registration of an orthostatic hypotension gives us important information for the rehabilitation strategy in patients after SCI. Paraplegic subjects
also had significantly lower baroreflex effectiveness and
greater blood variability, compared with the control
group (Castiglioni, 2007). Abnormal blood pressure
responses have been repeatedly described in these patients (Ditor et al., 2005). Therefore, a blood pressure
measurement for the basic assessment of autonomic
reactivity, in situations with different orthostatic load,
should be performed in patients after SCI. Frequency
analyses of autonomic function are related to clinical
measures of autonomic control after SCI and provide
useful noninvasive clinical tools with which to assess
autonomic completeness of an injury following SCI
(Claydon & Krassioukov, 2008).
DISCUSSION
CONCLUSION
Heart rate variability has been investigated during
postural stress as a means of identifying changes within
the frequency spectra corresponding to a sympathetic
stimulus (Vybiral et al., 1989) and vagal withdrawal. In
the able bodied population, increase in the low frequency component of heart rate variability was registered
and reported during postural stress and was associated
with significant reductions in the high frequency component, suggesting augmented sympathetic and diminished
vagal cardiac control (Montano et al., 1994).
Cardiovascular autonomic functions are markedly
disturbed in SCI patients. It can lead, as one of the
important factors, to an increase in mortality in these
patients.
Time domain, amplitude, and power spectral analyses were used to study HRV and autonomic functions.
The paraplegic subjects demonstrated a significant loss
of the low frequency component during 24-hour HRV
registration compared to able bodied controls. This was
interpreted as being consistent with predominantly sympathetic denervation uninfluenced by the degree of physical
activity (Bunten et al., 1998). The group with paraplegia
demonstrated a significantly lower HF baseline and LF
composite levels than controls (Grimm et al., 1997).
1. A decrease in the reactivity of the autonomic nervous
system to orthostatic changes, which evidences disturbances of cardiovascular regulation in patients
after spinal cord injury (paraplegics) was found.
2. The reduction of the low-frequency component (LF)
of the spectral analysis of heart rate variability reflects
a lowered sympathetic activity in these patients in
a sitting position. Furthemore, it reflects orthostatic
disturbances in situations with body position changes.
3. An examination of the blood pressure in different
body positions and the examination of autonomic reactivity by means of the SAHRV method contribute
to the checking of the autonomic dysfunctions in
patients after spinal cord injury.
Patient
1
2
3
4
5
6
7
8
9
10
mean
SD
A
6
8
8
8
10
6
8
8
7
7
7.6
1.11
B
9
7
7
6
5
8
7
5
7
8
6.9
1.22
C
1
1
1
2
1
2
1
3
2
1
1.5
0.67
Legend:
A – answers for sympathetic responses
B – answers for parasympathetic (vagal) responses
C – indifferent responses
ACKNOWLEDGEMENT
The study has been supported by the research grant
from the Ministry of Education, Youth and Sports of
the Czech Republic (No. MSM 6198959221) “Physical
Activity and Inactivity of the Inhabitants of the Czech
Republic in the Context of Behavioral Changes”.
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Acta Univ. Palacki. Olomuc., Gymn. 2010, vol. 40, no. 2
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Pagani, M., & Malliani, A. (1994). Power spectrum
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in sympathovagal balance during graded orthostatic
tilt. Circulation, 90(4),1826–1831.
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Salinger, J., Pumprla, J., Vychodil, R., Stejskal, P.,
Opavský, J., Novotný, J., & Bula, J. (1999). Microcomputer system for telemetric assessment of short
term heart rate variability in time and frequency
domain, type VariaCardio TF4. In A. Murray &
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Krejčí, J. (2005). Measurement of breathing frequency from ECG in the examination of autonomous
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SPEKTRÁLNÍ ANALÝZA VARIABILITY
SRDEČNÍ FREKVENCE U PACIENTŮ
S PORANĚNÍM MÍCHY
(Souhrn anglického textu)
VÝCHODISKA: Každoročně se v České republice
vyskytne 200–300 nových poranění míchy (SCI). Někteří z těchto pacientů trpí autonomními poruchami, jež
zasahují zejména jejich kardiovaskulární a genitourinární systém. Autonomní poruchy značně snižují kvalitu
života pacientů s SCI. U těchto subjektů je důležité posoudit závažnost postižení autonomní nervové soustavy
(ANS).
CÍL: Hlavním cílem této studie bylo posoudit spektrální analýzu variability srdeční frekvence jako indikátoru kardiovaskulární autonomní regulace u pacientů
s poraněním míchy a porovnat ji s nálezy zjištěnými
u zdravých kontrolních jedinců.
METODY: Této studie se zúčastnili paraplegici (průměrný věk 53,1 ± 15,8 let, sedm mužů a tři ženy). U pěti
z nich byla mícha poraněna částečně a u zbylých pěti
zcela. Byla použita klasifikace ASIA (American Spinal
Injury Association), modifikovaná Ashworthova stupni-
62
ce a Dotazník autonomních funkcí. Autonomní reaktivita byla hodnocena pomocí metody spektrální analýzy
variability srdeční frekvence (SAHRV; krátkodobá registrace) za použití testu leh-sed-leh (supine-sitting-supine).
Byl použit diagnostický systém VarCor PF7, což je inovace systému VarCor PF6. Kontrolní skupinu tvořilo
dvacet čtyři subjektů (průměrný věk 51,9 ± 9,4 roku).
VÝSLEDKY: U pacientů po SCI (paraplegiků) byl
v rámci reakce na ortostatické změny zjištěn výrazný pokles reaktivity autonomní nervové soustavy. Ve srovnání
se zdravými kontrolními jedinci byly u těchto pacientů během změn pozice těla potlačeny zejména charakteristické reakce nízkofrekvenčních (LF) a vysokofrekvenčních
(HF) spektrálních složek. Navíc byl u těchto pacientů
zaznamenán významný pokles spektrálního výkonu u LF
a HF složek. Hodnota celkového výkonu (TP) spektra
byla výrazně nižší ve skupině paraplegiků ve srovnání se
zdravými dobrovolníky, a to jak při první pozici vleže,
tak i při opakovaných pozicích vleže. Významná míra
ortostatické hypotenze byla zaznamenána pouze u dvou
paraplegiků v poloze vsedě. Menší zvýšení poměru
LF/HF bylo zaznamenáno v poloze vsedě ve skupině
paraplegiků ve srovnání se zdravými jedinci.
ZÁVĚRY: U pacientů s poraněním míchy (paraplegiků) byl zjištěn pokles reaktivity autonomní nervové
soustavy na ortostatické změny, což dokazuje poruchy
kardiovaskulární regulace. Snížení nízkofrekvenční (LF)
složky spektrální analýzy variability srdeční frekvence
u těchto pacientů reflektuje sníženou sympatickou aktivitu v poloze vsedě. Odráží ortostatické poruchy v situacích, kdy se mění poloha těla, což je spojeno se změnou
ortostatického zatížení. Přesnější hodnocení autonomní
dysfunkce u pacientů po SCI je podpořeno měřením
krevního tlaku a SAHRV.
Klíčová slova: poranění míchy, spektrální analýza, variabilita srdeční frekvence, autonomní nervová soustava.
Acta Univ. Palacki. Olomuc., Gymn. 2010, vol. 40, no. 2
PhDr. Petr Uhlíř
Palacký University
Faculty of Physical Culture
tř. Míru 115
771 11 Olomouc
Czech Republic
Education and previous work experience
2000 – Faculty of Physical Culture, Palacký University
Olomouc, Department of Physiotherapy, Master Degree
in Physiotherapy.
2000 – cont. – Faculty of Physical Culture, Palacký University Olomouc, Department of Physiotherapy, Assistant.
2005 – Faculty of Physical Culture, Palacký University
Olomouc, Kinanthropology, PhDr.
Scientific orientation
1. physiotherapy.
2. rehabilitation.
3. heart rate variability.
First-line publications
Uhlíř, P., & Opavský, J. (2005). The influence of reflex
massage on heart rate variability. In Proceedings
of the 4th International Conference Movement and
Health. Olomouc: Palacký University.
Uhlíř, P., & Opavský, J. (2006). Vliv reflexní masáže
na autonomní regulaci variability srdeční frekvence.
In D. Smékal & J. Urban (Eds.), 1. absolventská konference katedry fyzioterapie Fakulty tělesné kultury:
Sborník abstraktů (pp. 55). Olomouc: Univerzita
Palackého.
Uhlíř, P. (2008). Pohybová cvičení seniorů. Olomouc:
Univerzita Palackého.